#include<stdio.h>
int main()
{
int n;
scanf("%d\n",&n);
if(n > 0 && n <= 2)
{
printf("1");
}
else
{
int i,sum,a=1,b=1;
for(i = 3;i<=n;i++)
{
sum=a+b;
a=b;
b=sum;
}
printf ("%d",sum);
}
return 0;
}

